الفهرس 
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Abstract
The mechanical properties of epoxy reinforced by chopped strand mat fibers and its nano composites were studied. Also, the fracture behavior of these composites was studied using the essential work of fracture method (EWF). The reinforcement used was: chopped glass fibers (weight fraction: 50%), two inorganic materials nano-SiO2 (nanosilica) 12 nm diameter, and carbon nanotubes (have outer diameter of 40 nm, length of 5 μm and the number of walls between 3 and 6) were used as toughening materials. Glass Fiber Reinforced Polymer GFRP composite laminate was manufactured using commonly hand layup technique. Nano-silica particles SiO2 with concentration 5, 10, 15 and 20 wt. % of total composite weight and multi-walled carbon nanotubes 0.5 wt. % of total composite weight are used for the preparation of the composites. The dispersion of nano particles in the epoxy resin was studied using Transmission Electron Microscope. Also, the fracture surface of the investigated specimens was studied microscopically using Scanning Electron Microscopy (SEM). The effect of adding nano-silica on the Young’s modulus, tensile strength and failure tensile strain was studied. The results illustrate that the addition of nano-fillers into the GFRP composites produced an increase in the Young’s modulus and tensile strength without reducing the failure strain even at high nano-silica content compared to the neat GFRP. Young’s modulus of 3.30 GPa was measured for the neat GFRP while a maximum Young’s modulus of 4.65 GPa was measured, for the GFRP with 15 wt. % of 12 nm silica particles. This showed an increase of about 41 % compared to that of neat GFRP composite.
A maximum tensile strength of 322.6 MPa was measured, for GFRP with 15 wt. % of nano-silica particles, which is an increase of about 77.9 % compared to that of the neat GFRP.
Tensile strength and failure tensile strain values are significantly improved by adding multi walled nano carbon tubes compared to 15 wt. % SiO2 GFRP composite.
from the results of fracture test using Essential work of fracture method (EWF) it can be seen that, for the range of ligament lengths studied (8<L<16mm), the variation of wf with L is basically linear and the silica particles concentration level has a significant effect on wf testing results compared with neat GFRP. Also, it was found that wf has a great increase for GFRP with 15 wt. % silica particles concentration level. However, with further increase of silica content (20 wt. %), wf slightly decreases. The specific non-essential work of fracture of GFRP/nano-SiO2 has also increased with silica particles concentration level increasing from 0 wt. % to 15wt. % then has a little decrease. Also, the effect of adding (nano-carbon tubes 0.5wt. %) on the specific work of fracture wf of GFRP/SiO2 (15 wt. %) composite was studied it can be seen that the result compared with that of neat GFRP, shows that wf of GFRP with 15 wt. % silica particles was significantly improved with the addition of 0.5wt. % nano-carbon tubes. These results indicate that MWNCTs + SiO2 toughen the matrix effectively.
The effect of ligament/width ratio on the yield strength of GFRP and its nano composites was studied. It was found that the neat GFRP the yield strength has a slight decrease with increase L/W ratio especially at 20% L/W then its value increases. While in (5, 10, 15 wt. % SiO2 and 15 wt. % SiO2 + 0.5 wt. % MWNCTs) the yield strength increases with increase L/W ratio. Also, the value of the yield strength at the same L/W ratio increases with increase nano fillers in the epoxy matrix until it reaches its maximum value at (15 wt. % SiO2 + 0.5 wt. % MWNCTs) composite. It’s notable that the yield strength of 10 and 20 wt. % SiO2 has a convergent values.
The particles distribution of nano-particles filled composites was examined using Transmission Electron Microscope (TEM), Fractographic observations were investigated using Scanning Electronic Microscope (SEM) to study the influence of nano-silica and carbon nanotubes on the fracture behavior of GFRP.